2: From Molecular to Human Movement

Question 1

Describe the sliding filament theory?

Answer 1

The MU is stimulated by nerve that causes a flush of calcium into the sarcomeres

Troponin binds with the calcium, this causes a displacement of the tropomyosin and freeing myosin binding points

The myosin heads at this point are bound to ADP and a free phosphate. The heads release the free phosphate and bind to the binding points on the actin.

Then a power stroke occurs as the heads pull the actin and mysoin together. Whilst doing this they release the ADP

ATP is then bound to the myosin heads to stop the movement and sever the connection.

As they move back into starting position, the myosin head breaks down ATP into ADP and a free phosphate. the energy released from the breakdown is stored in the heads ready for the next power stroke.

Question 2

How does cross bridge cycling influence force and velocity?

Answer 2

The more myosin heads attached to the actin filament the greater the force

The faster the rate of cross bridge cycling the greater the muscle shortening velocity.

Question 3

If a sarcomere length is fixed, and the number of cross bridges are constant, what happens when you stretch the sarcomere?

Answer 3

Eccentrically stretching the sarcomere induces a large spike in force. As you release the tension the resting force is still greater than a non stretched sarcomere. This is due to molecules and chemicals within the sarcomere

Question 4

Why do long fibres, with more sarcomeres in series contract more quickly?

Answer 4

increased distance but time to shorten is the same- velocity= distance/time

Question 5

Describe the force-length curve for differentstatic measurements of sarcomere lengths ?

Answer 5

The graph displayed a optimal resting length for a sarcomere (2.6um). Either side of this the producable tension (% of maximum) decreases.
The descending limb refers to the thin and thick filaments are too stretch apart, therefore not enough binding sites are available.

the ascending limb refers to when thick and thin filaments are compressed together. They overlap and interfere, blocking binding sites.

greater stretch or compression decreases %tension.

Normal range: 1.6-2.6

Question 6

Why do things don’t add up from sarcomere to whole muscle?

Answer 6

for a fixed length of muscle fibre, you may have a variation in the number of sarcomeres.

This changes the force-length relationship and makes it more curvilinear. As well as changing the min and max length where force is producible.

Question 7

What are the two benefits or a curvilinear relationship?

Answer 7

1) being able to stretch out the right hand side of the graph is safe- can produce force when muscle is being stretched.
2) Increases the range over which force can be produce.

Question 8

Who cares about force-length relationship in sport and why?

Answer 8

Depending on how long your muscle fibres are, and the position you’re in, will determine the force can you produce.

The standard operating length of fibres during running and cycling are on different limbs.
- runner receive large eccentric loads with each step. The graph previously shows with a fixed amount of cross bridge attachments an eccentric pull will increase force output. Therefore, within the more ascending side of the relationship, there more cross bridge attachments and thus more tension available.

Cylists work on the descending side of the relationship as eccentric loading is not an issue and rate of cross bridge cycling is imperative to performance.

Question 9

Describe the force-velocity graph for concentric muscle?

How is this tied with force-length? and power output?

Answer 9

Hyperbolic curve.

Greater force required, slower the contraction and vise versa.

Force is dependant on the length of the muscle fibres and the speed of the muscle fibres shortening

maximal power output occurs at 1/3 velocity shortening velocity.

Question 10

What the differences in concetric and eccentric muscle properties?

Answer 10

Concentric contractions require a lot of ATP whereas eccentric use minimal ATP. ATP is used to detach the myosin heads, if eccentric stretching is pulling of myosin heads, they do not require ATP.

Concentric produce high levels of EMG per unit of force whereas Eccentric EMG signals are not as large.

More force during eccentric muscle contraction. If cross bridges are being stretched they are producing more force.

As you start to stretch a muscle eccentrically, a steep resistance and increase in force is observed, then we see a plateau.

Question 11

In practice, the theory behind greater strength during eccentric stretching does not occur. Why?

Answer 11

Our bodies do not require such large forces in real life.
Our surrounding tissues (tendons and bones) would need to be bigger and stronger, thus requiring more upkeep energy and tissues- this is inefficient.

However, in smaller muscles this relationship can be observed.

Question 12

Why are we naturally stronger during Eccentric resisting?

Answer 12

if you have equal concentric and eccentric strength, and jump up from the floor maximally, the force you land on will be greater due to gravity. Further if you jump from a platform, you will land with greater force than you can produce. So having greater resisting force is safe.

Question 13

How can Eccentrics be used in training? An

Answer 13

You can use eccentrics to attain higher rep ranges or higher absolute loads. But doing same amount of reps as concentric will not elicit greater muscle fibre use or growth

Eccentrics also increase doms

Question 14

Where is connective tissue found in a muscle

Answer 14

Endomysium- Around the muscle
Perimysium- around muscle fibre bundles, fascicles
Epimysium- around whole muscle

Question 15

Why are the effects of passive tissues more resonant toward the end of ROM?

Answer 15

As a muscle is stretched, the passive tissue is also stretched and provides eccentric force

Passive tissue also becomes stiff to prevent the muscle from over stretching

Question 16

In what locations is having passive tissue a good or bad thing?

Answer 16

Good- around the spine to stop the overstretch of supporting muscles

bad- prevent range of motion in muscles with large ranges such as bicep.

Question 17

How does passive tissue provide force to contraction?

Answer 17

they have to be stretched first (eccentrically). They then spring back with great force.

Question 18

What are the difference in properties between long and thin, and thick and short muscle?

Answer 18

short muscle can produce greater force but within a narrow range of length. Long muscle can produce less strength but over a greater range of lengths.

During concentric contraction- short muscle is stronger isometrically, but long muscle can produce force at much greater velocities, therefore can produce power over greater range.

peak power is the same

Question 19

What does the table of properties look like for long vs thick muscle:

Contraction time
Max force
ROM
Max Velocity
Max Power

Answer 19

Contraction time Long=Thick

Max Force - Long < Thick

ROM- Long > Thick

Max Velocity- Long > Thick

Max Power - Long = Thick

Question 20

What different properties between straight muscle and penated muscle are there?

Answer 20

Parallel- when fibres shorten the muscle belly shortens in the same direction, the same distance and the same speed.

Pennate- Fibre shortens, the muscle belly shortens less as some shortening occurs perpendicular to tendons. Greater number of fibres can fit within a given size of muscle.

There is a trade off between shortening velocity or shorten over a longer range for a greater peak force over a shorter range at low velocities.

Question 21

What is the limiting pennation angle?

Answer 21

45 degrees, above this- more force would be applied perpendicular to the tendons

Question 22

What are the two ways of measuring muscle volume?

Answer 22

Normal CSA and physiological CSA

PCSA is cut in the direction of the muscle fibres.
PCSA is typically bigger than the CSA
PCSA is more important when measuring force generating capability

Question 23

Why if a muscle have 3x greater volume would its force not be 3x greater?

Answer 23

Fibre length and pennation angle of the fibres determine force to a greater extent than sheer volume

Question 24

What did the motor unit slide say?

Answer 24

Alpha motor neuron plus the fibres associated with it

Fibre to neuron ratio varies due to location as well as over time
- age, injury

Question 25

For a given stimulation, what are the differences in fast and slow twitch muscle fibres?

Answer 25

fast twitch can reach far greater velocities. therefore force can be produced over a greater range of velocities.

Fast twitch are physically bigger, therefore stronger (greater CSA)

Question 26

What two factors with stimulation can effect muscle force?

Answer 26

Rate coding - more frequency of fibres builds up more strength

Motor Recruitment- more fibres, more strength

Question 27

What is hennemans size principle?

Answer 27

Steady increase of motor unit recruitment. The smaller, less fatiguable type 1 fibres are recruited first and then followed by bigger more fatiugable type 2a&x fibres

Question 28

what is the difference between contraction and relaxation in a muscle?

Answer 28

relaxation takes twitce as long in some cases.

Better athletes can relax their muscles quicker

Question 29

What is tetani?

Answer 29

muscle fibres are being continulaly stimulated so were continually contracting.

• this process takes time
• single stimuli need to overlap and flood the muscle with calcium
• a point is reached where stimuli are overlapped and a constant force is given.

Anything talking about isometric testing measure force under tetanic conditions.
180ms is average time to reach tetanus

Stimuli must be sent at 20-30 Hz minimum. Can be sent quicker to reach tetanus quicker.